Polyethylene glycol bis(allyl carbonate) resins represented by CR-39 (trade name, produced by PPG) or diallyl phthalate-based compounds are advantageous in that since the polymerization reaction proceeds at a low speed as compared with acrylic resins, the polymerization reaction is easy to control and a uniform polymerization reaction can be attained. As a result, plastic lenses derived from polydiethylene glycol bis(allyl carbonate) esin or from diallyl phthalate-based compound are educed in the optical strain.
As for polyvalent (meth)allyl esters derived from trivalent or greater polyvalent carboxylic acids, triallyl 1,2,4-benzenetricarboxylate (e.g., TRIAM-705, trade name, produced by Wako Pure Chemical Industries, Ltd.) is known.
However, the refractive index of the cured product of triallyl 1,2,4-benzenetricarboxylate is 1.57 or less and this is excessively low for the refractive index of high refraction lens materials. Furthermore, the cured product is low in impact resistance, and therefore this ester cannot be used as a main component of high refraction plastic lens materials.
As means for dealing with this problem, allyl esters having an allyl ester group at the terminal and internally having the following structure which is derived from a polyvalent saturated carboxylic acid and a polyvalent saturated alcohol, are also known:CH2═CHCH2O{CORCOOB′O}nCORCOOCH2CH═CH2 wherein R represents a divalent organic residue having from 1 to 20 carbon atoms, B′ represents a divalent organic residue derived from a diol, and n is a number from 1 to 20.
These allyl esters provide a cured material having excellent impact resistance. However, since an aliphatic hydrocarbon B′ is used inside, even if a terephthalic acid or an isophthalic acid is used as the polyvalent saturated carboxylic acid, the refractive index becomes lower than that of the cured material of diallyl terephthalate monomer or diallyl isophthalate monomer itself. As such, the refractive index is not necessarily satisfactory in use for high refractive index lenses.
Also, a plastic lens composition containing an organic residue derived from a compound having an aromatic ring and two or more hydroxyl groups is proposed in Japanese Unexamined Patent Publication No. 7-138334 (JP-A-7-138334).
In the composition of JP-A-7-138334, the low viscosity cannot be attained unless the amount of the compound having an aromatic ring and two or more hydroxyl groups used is greatly reduced or the reactive monomer is used in a large amount. However, if the amount of the compound having an aromatic ring and two or more hydroxyl groups used is drastically reduced, a high refractive index of 1.58 or more cannot be obtained. Furthermore, if the reactive monofunctional monomer is used in a large amount, the heat resistance disadvantageously deteriorates. Under these circumstances, an ester usable as a main component of lens materials having high refractive index, low viscosity and low specific gravity is in demand.